1. Field of the Invention
The present invention relates to a radio communication device comprising a receive path having first rf-processing means, a transmit path having second rf-processing means, an antenna for receiving and transmitting a radio signal, a transmit-receive switching means coupled between the antenna and the receive and transmit path for switching the antenna to the receive path when the radio communication device is in a receive mode and for switching the antenna to the transmit path when the radio communication device is in a transmit mode, and power supply means for selectively supplying power to the first and second rf-processing means when the radio communication device is in the receive mode or in the transmit mode, respectively. Such a radio communication device can be a cellular or a cordless telephone, or any other suitable two way communication device. The radio device is arranged for alternately receiving or transmitting.
2. Description of the Related Art
A radio communication device of the above kind is known from the handbook "Cordless Telecommunications in Europe", H. W. Tuttlebee, pages 213, 219, and 223, Springer-Verlag London Ltd., 1990. At said pages various transceiver structures are disclosed with different implementations of coupling the antenna to the transmit path or to the receive path, when the transceiver is in transmit mode or in receive mode, respectively. In the transceivers described on page 213 and 219, antenna duplex filters are used for such an antenna coupling. In the transceiver described on page 223, a transmit-receive switch is used. In the latter transceiver actuating of the transmit-receive switch is only shown schematically. Usually such switches are electronic switches, although also costly coaxial transmission line based switches have been used. Using a duplex filter causes insertion losses in both the transmit and receive path. Due to such an insertion loss up to half or even more of the transmit power is lost in the filter, and the receiver sensitivity is degraded considerably. To compensate for such losses additional amplification is needed so that power consumption is increased. Furthermore, a good low loss duplex filter is a costly component. Use of an electronic switch, which is a non-linear element, causes undesired harmonic distortion. An electronic switch is also a lossy component with a limited operating voltage range. Given a desired rf-power, within such a limited voltage range, the current has to be higher so that there is an increased need for matching circuitry. Due to a higher current, there is an increased loss in printed circuit board wires. In practical cases, use of an electronic switch necessitates the use of a filter in the transmit path to limit transmit noise and harmonics generated in the switch. Also, a filter in the receive path is needed to obtain the necessary band selectivity. When applying a switch based solution, however, the requirements as to attenuation in the transmit band and power requirements are less demanding then applying a duplex filter based solution. So, after all, a switch based solution is beneficial. In modern lightweight communication devices, such as TDMA (Time Division Multiple Access) based digital cellular radio devices and cordless phones, it is highly desirable to reduce power consumption as much as possible because of the desire to have long standby and talk times. For this reason, circuitry in the receive and transmit path is switched off when not needed from a functional point of view. Also the rf front-end should be as linear as possible to that frequency spectrum requirements can be fulfilled more easily.